PYEONGCHANG, South Korea — Russian curler Alexander Krushelnitsky has been charged with a doping offense at the Pyeongchang Olympics.

Krushelnitsky, who won bronze in mixed doubles with his wife Anastasia Bryzgalova, tested positive for meldonium, Russian officials said Monday.

Here are some of the key issues surrounding meldonium:

Q: What is meldonium?

A: A Latvian-made drug available over the counter in Russia and other Eastern European and former Soviet countries, often without a prescription. The drug’s manufacturer, Grindeks, says it is mostly aimed at people with heart conditions, though it can also be used for “physical and psycho-emotional overload” in otherwise healthy people. Meldonium’s inventor, chemist Ivars Kalvins, has said it was given to Soviet soldiers fighting in Afghanistan to boost their stamina. However, Grindeks and Kalvins have argued it shouldn’t be banned in sports, with the manufacturer saying that it “cannot improve athletic performance, but it can stop tissue damage” during intense exercise. Meldonium is usually known by the brand name mildronate, though other names have been used.

Q: Why was it banned?

A: The World Anti-Doping Agency said in September 2015 that meldonium would be banned as of Jan. 1, 2016, and published information on its website. A study conducted at the European Games in June 2015 and later published by the British Journal of Sports Medicine found 66 of 762 athletes taking meldonium, which the authors called “excessive and inappropriate use … in a generally heathy athlete population.” It was offered to Russian national teams in numerous sports, and was believed to help athletes tolerate tough training workloads.

Q: Who else tested positive?

A: Tennis player Maria Sharapova is the most famous person to be banned for meldonium, serving a 15-month sanction after testing positive at the 2016 Australian Open. Shortly after meldonium was banned, there were more than 170 failed tests by athletes, almost all from Eastern European countries, including Olympic medalists in sports ranging from figure skating to wrestling. Heavyweight boxer Alexander Povetkin had a title fight called off for a positive test. There have been few cases since 2016, though the Russian national junior women’s handball team was disqualified from last year’s European championships when three players tested positive.

Q: What has happened to athletes who tested positive?

A: Almost all of the early cases were dropped when athletes insisted they had stopped taking meldonium in 2015, before it was banned. The usually low concentrations of the drug in their samples backed up those arguments, and WADA accepted findings of “no fault or negligence” in those cases. However, anyone taking meldonium after the January 2016 cutoff date faces the same potential penalty — a ban of up to four years — as for any other banned substance. Sharapova’s 15-month sanction was lower than the maximum, partly because the Court of Arbitration for Sport accepted she hadn’t known meldonium was banned.

Q: What next for Krushelnitsky and Russia?

A: The Court of Arbitration for Sport has yet to set a date to hear his case. If he is found guilty, he could be banned and forced to return his Olympic bronze medal. The International Olympic Committee could decide against formally reinstating Russia for the Pyeongchang closing ceremony, meaning its athletes would not be allowed to march under the Russian flag.

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